A seat belt retractor has a winding spring biasing a belt reel in the belt winding direction to pull the belt taut about the occupant. A first inertia-sensing means is adapted to sense a predetermined level of vehicle deceleration and lock the belt reel against belt unwinding rotation to restrain the occupant in the seat. Ratchet teeth carried by the reel in the belt winding direction are selectively engageable by a detent member. A control means is operable to move the detent member to a detenting position engaging ratchet teeth to prevent winding of the reel and thereby relieve the belt tension on the occupant by establishing a slackened belt condition about the occupant. A second inertia-sensing means senses a predetermined level of vehicle deceleration less than the level sensed by the first inertia-sensing means and is adapted to move the detent member to the undetenting position to restore the winding effort of the winding spring and pull the belt taut against the occupant prior to locking of the belt reel against belt unwinding rotation by the first inertia-sensing means.

Improvements in a retractor for seat belt are disclosed. The improved retractor for seat belt comprises a particular and simple cam plate having three differently shaped guide surfaces for guiding a ratchet engageable with a ratchet wheel to prevent the webbing taking up rotation of a webbing take-up shaft.

A spindle is supported for rotation in opposite directions about its longitudinal central axis. An end portion of seat belt webbing is secured to the spindle. The belt webbing normally moves parallel to a predetermined plane as the belt webbing is withdrawn from the spindle. The belt webbing moves in a direction transverse to the predetermined plane during the last quarter of a revolution of the spindle as the belt webbing is fully withdrawn from the spindle. The spindle is biased to rotate about its longitudinal central axis in a belt retraction direction to wind the belt webbing onto the spindle. A comfort mechanism has a member which is movable between a first position in which rotation of the spindle in the belt retraction direction is blocked and a second position in which rotation of the spindle in the belt retraction direction is permitted. A release mechanism moves the member of the comfort mechanism to its second position in response to the end portion of the belt webbing moving in the transverse direction relative to the predetermined plane during the last quarter revolution of the spindle as the belt webbing is fully withdrawn from the spindle.

A seat belt retractor for motor vehicle applications having a switch assembly for controlling a seat belt warning indicator or other electrical circuits requiring an input of belt webbing extension or retraction. The switch assembly includes a cam disk which is rotatable with the retractor spool having generally spiral grooves on one of its radial face surfaces. A follower, made of an electrically conductive material, engages the grooves and is moved radially in response to the rotated position of the spool. When the follower reaches a predetermined radial position, the follower engages the electrical contacts, thereby closing an electrical circuit.

A retractor for seat belt with an alleviating device has a webbing take-up shaft biased in webbing take-up direction and rotatably supported on a base, a gear train comprising a first gear member mounted on the take-up shaft for rotation therewith and a second gear member mesh-engaging the first gear member and rotatably provided on the base, a disc with a cam portion provided for rotation with the second gear member by friction engagement therebetween, and a latch member movable between an engaged position in which it is engaged with a portion integral with the gear train and prevents the rotation of the take-up shaft in the webbing take-up direction and a disengaged position in which it is not engaged with the portion integral with the gear train. The latch member is biased toward the engaged position, and the disc with a cam portion has a first guide portion for guiding the latch member from the engaged position to the disengaged position upon draw-out of webbing, a second guide portion for guiding the latch member to the disengaged position upon take-up of the webbing and for holding the latch member in the disengaged position, and a third guide portion for guiding the latch member held in the second guide portion to the engaged position upon draw-out of the webbing.